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R. A. FESSENDEN METHOD FOR ELIMINATING UNDESIRED IMPULSES Filed Nov. 101920 40 4/ 42 3/ 26 :H m m r.

WITNESSES: 11v VENTOR.

i a'tented Nov. 6, 1923.

REGINALD A. FESSENDEN, OE CHESTNUT HILL. MASSACHUSETTS, ASSIGNOR 'I'OSUB- MARINE SIGNAL COMPANY, OF PORTLAND, MAINE, A CORPORATION OF lhAINE.

METHOD FOR ELIMINATING UNDESIRED IMPULSES.

Application filed November 10, 1920. Serial No. 423,184.

To all whom, it may concern.

Be it known that 1, Rnomiuln A. FES- SENDEN, of Chestnut Hill, in thecounty of iMiddlesex and State of Massachusetts, a citizen of the UnitedStates, have invented new and useful Improvements in Methods forEliminating Undesired impulses, of which the following is aspecification My invention relates to methods and apparatus foreliminating undesired impulses and more particularly to eliminatingdisturbing impulses, such as noises and static in signaling circuits.

My invention has for its object greater efficiency in the elimination ofsuch disturbing impulses and more particularly greater" in 28, Fig. 2,where the undesired impulse 31 efiiciency in signal reception.

- Figures 1, 2, 3, 1 and 5 show, partly diagrammatically, arrangementssuitable for carrying out my invention.

In Fig. 1, 14: is an antenna grounded at 25. The circuits l4, l2, l6,18, 21, :25 and l4, l3, 17, 19, 22, 25 are both tuned to the desiredsignals, the inductance 16 being larger than the inductance l7 and thecapacity 15 being less than the capacity 19.

21 and 22 are any receiving devices, for example the filaments of twofilament galvanometers, connected so that their indications or movementsare in opposite directions, as shown by the arrows, and oppose eachother, eti ected, for example, in the case of the filaments, by joiningthem with a light bar :24.

On the reception of a mixture of desired signals andundesired impulseson the antenna lithe desired signals will divide ;uhstantially evenlybetween the two circuits and there will be no movement of the bar 2%.

Undesired impulses received on the antonne. 14 will, however, distributethemselves unevenly between the two circuits on ac count of thedifferent amounts or inductance and capacity in the two circuits, andcon- Sequently will roduce movement of the bar 24, a recor of which(:27) is shown in Fig 2. l

14, 15, 20 and 25 is a third c1rcu1t which is substantially untuned andcontains the ad'ustable ohmic resistance 15, and thegalvanometenfilament Gonsequently the indication produced by thelvanometer filament 20 if it were free wen ti that'represented hv therecord 26 -comparedi. 0., the record 27 made by the bar 24 and therecord 26 made by the. filament 20, the fact that 29 is a disturbingimpulse and not a signal is at once apparent and the message can beread.

This may also be done directly by attaching the filament 20 to the bar24 by a second bar 23 in such a direction that the motions are opposedto each other, as shown by the arrows.

in this (Vise the record produced b Y the motion of the combined barwill he as shown is substantially cut out.

In Fig. 3 is shown a variation of this method, in which-3; 33 arecircuits tuned to the desired signals and 32, 32 are circuits tuned to afrequency below that of the desired signals and ll, 34' circuits tunedto a frequency above that of the desired signals. 45, 16, aregalvunometer filaments tending to move in the direction of the arrowsand connected by the bar 47 and grounded at 35.

' In this case the filament to will be acted on by a force producedsubstantially only by t e undesired impulses, since substantially allthe desired signals will be led to round without affecting the filament46, )n the other hand the filament 46 will be acted upon by a force due.to the sum of the undesired impulses and the desired nuls. Consequently,since the filaments are connected together by the bar it and tend tomove in opposite direction, the resultant motion of the bar 47 sidewayswill be due to the signals alone.

Fig. 4 shows another modification in which the circuits 32, 32, 323, 33,34-, Ill and the filaments are as stated above, but the oil cult 33,instead of being connected to ground, is connected through a resistance48 to the galvunometer filament l6. This ohmic resistance 46 ispreferably made to have such value that the circuit 33, 48 is largelydeadbeat to the desired signals, so that substantially all, or a largepart, of the energy of the desired signals is absorbed in this circuit,Whereas it is not so largely absorbed in. the circuit 33.

'For the sake of simplicity I have shown In Fig. 5, the circuits,comprising the in ducta-nces 1 6, 17, 16, 17, capacities 18, 19, 18',19, resistances 50, 51', 50, 51, trans former primaries 53, 54, 53,5-1', f and grounds 35, 35, are all. tuned to the desired signals, butthe circuits containing the in--' ductances 16 and 16' have moreinductance and less capacity than the circuits containing theinductances 17 and 17.

The resistances 50, 51, 50, 51 are all originally equal but theresistances 50' and 51 are variable. v

The circuit containing the transformer secondaries 55, 55 and the iridicating instrument 56 is connected so that the transformer primaries53, 54. oppose their effect on the secondary 55 andthe transformerprimaries 535, 54' oppose their effect on the secondary '55.

In operation the desired signals are first sent and the circuitsadjustedj'until no signal is detected in. the deter-turbo.

Then the undesired distuizlsung impulses are listened in to and thecircuits adjusted until no indication is producedfin this case also onthe indicator 56.

I. e., neither desired signal or the undesired impulses prmluee any 1mnerefon on 56.

Then the resistance 50' is slightly altered indication produced by 56will be mainly due to the desired signals, especially if 51 is alsoaltered, to balance out the remainder of the undesired impulses.

It will, of course, be understood'that a I number of such sets ofdevices may be used in series with each other, thereby producing asuccessive strengthening, of/the ratio of the desired signals to theundesired impulses, and also other instruments Well known in the art,for example amplifiers, may also be used.

The object of making the resistance 15,

Fig. 1, variable is to assist in balancing the opposing indications,This may also be done by 'any equivalent means-for example by insertingadjustable 'an'iplifiers in the circuits 16, 18 and 17,19.

\Vhat I claim is:

In a system of signaling the method of. eliminating disturbing noises,which con sists in receiving the disturbing noises more effectively thanthe signals which it is desired to receive, on one portion of thereceiving' system, recording the indications as re ceived, and receivingsaid (llStllI'blIl noises and desired signals in a more equally CfieC-tive manner on another pprtion of said receiving system, and recordingthe indlcatioiis so received, and detecting and eliminating thedisturbing effects by comparison of said records.

REGINALD AQFESSENDEN.

